The present invention relates to self-extinguishing polystyrenic compositions and to their preparation. More particularly, the invention relates to the improvement of the thermal stability properties of these compositions.
It is well known that styrenic resins, such as rubber reinforced polystyrene, acrylonitrile-butadiene-styrene resins, and polystyrene foams, may be rendered self-extinguishing by incorporating a halogenated organic compound therein. However, the action of this halogenated organic compound alone is generally not sufficient to make the styrenic resin fire-resistant, and a synergistic agent such as a peroxide or antimony trioxide is concomitantly used together with this halogenated organic compound.
In order to avoid the use of these synergistic agents, it has been suggested to use as fire-retardant agents, halogenated organic compounds which are less thermally stable. The advantage of these compounds resides in the fact that they are used alone and in lower amounts.
However, when styrenic resins containing such a type of fire-retardant agent are submitted to an injection molding process, wherein temperature generally varies from about 200.degree. to 300.degree. C., thermal decomposition of the fire-retardant agent occurs and this decomposition has a deleterious effect on the properties of the resin.
In order to overcome this drawback, thermal stabilizers are usually introduced into the composition. These stabilizers are generally compounds of barium, cadmium, lead or tin. However, these thermal stabilizers have a deleterious effect on the fire resistance. The only means to overcome this additional drawback is to increase the fire-retardant agent concentration in the composition, and hence the cost of the product.